Oxidized celluloses (or oxycelluloses) are water insoluble materials produced by reacting cellulose with an oxidant such as gaseous chlorine, hydrogen peroxide, peracetic acid, chlorine dioxide, nitrogen dioxide (dinitrogen tetraoxide), persulfates, permanganate, dichromate-sulfuric acid hypochlorous acid, hypochlorous acid, hypohalites or periodates. These oxidized celluloses may contain carboxylic, aidehyde, and/or ketone functionalities, in addition to the hydroxyl groups, depending on the nature of the oxidant and the reaction conditions used in their preparation.
The treatment of cellulose with alkali and alkaline earth metal hypochlorites has been studied to establish conditions that prevent damage of cellulose fibers during various industrial processes involving or modifying grade cellulose products. Working with different grades of cotton cellulose fabrics, Clibbens et al. J. Textile Inst., 18, T135 (1927) note that the oxidation of cellulose by hypochlorite occurs more rapidly at a neutral pH, and in the presence of high concentrations of alkali (i.e., about 2-5N sodium hydroxide), than under mild acidic or basic conditions. The rapid increase in the oxidation rate with an increase in the alkali concentration is attributed to the increased mercerizing action of the sodium hydroxide. According to M. Lewin and J. A. Epstein J. Polymer Sci., 58,991 and 1023 (1962), the amount of carboxylic groups in the product decreases, whereas the aldehyde and ketone contents of the product increase with a decrease in the pH of the reaction mixture (from a pH of 10 to pH 5). Other studies indicate that oxidized cellulose products prepared under mild acidic conditions degrade and turn yellow during storage, whereas those prepared under basic conditions are quite stable [see T. P. Nevell, in Cellulose Chemistry and its Applications: 1. Cellulose, T. P. Nevell et al., eds., Ellis Hardwood Ltd., England (1985) at Ch, 10.].
U.S. Pat. No. 3,111,513 discusses the preparation of mixed carboxylic and aldehyde containing oxidized cellulose derivatives by reacting cellulose crystalline aggregates, prepared by treatment of the original cellulose material with 2.5N hydrochloric acid at boiling temperature for 15 minutes, with aqueous sodium hypochlorite solution at pH 7 and 9. The product of the reaction at pH 9 contained a higher carboxylic and a lower aldehyde content than the product formed at pH 7.0. The starting crystalline cellulose material had a level-off degree of polymerization value of 220.
The preparation of oxidized celluloses suitable for use as carrier vehicles in the development of cosmetic and pharmaceutical preparations, using alkali metal or alkaline earth metal hypohalites, is discussed in U.S. Pat. No. 4,480,089. The method involves treating a fibrous cellulosic material with a hypochlorite solution having an initial pH of about 12, at a temperature of 15.degree.-60.degree. C., and allowing the pH to drop to about 2. The method appears to produce mixed carbonyl containing oxidized cellulose derivatives. The products thus tend to change color and rapidly change color during storage in the presence of amine drugs.
Accordingly, an object of the present invention is to provide a method whereby a stable oxidized cellulose product, can be prepared from cotton linters, wood pulp and like materials. Another object is to produce an oxidized cellulose product stable to color change during storage, and compatible with a wide variety of chemicals and drugs.
A further objective of the present invention is to provide an oxidized cellulose material suitable for use as an excipient for preparing solid and semi-solid formulations having applications in cosmetic, pharmaceutical, agricultural, and consumer products development.